Method to pressurize sic fuel cladding tube before end plug sealing by pressurization pushing spring loaded end plug

A nuclear core component having a tubular cladding with an upper and lower end respectively sealed by an upper end plug and a lower end plug, a lower portion of an interior of the cladding housing an active element with a spring extending between the upper end plug and the active element to bias the active element toward the lower end plug, the upper end plug comprising:

• an upper end plug external piece and an upper end plug internal piece, the upper end plug internal piece configured to slide within a through opening in the upper end plug external piece and have a lower end that biases the spring towards the active element when the upper end plug forms a gas tight seal at an interface of the cladding and the upper end plug, at least partially closing off the upper end of the cladding, the through opening and the upper end plug internal piece configured so an upper portion of the upper end plug internal piece fits within the through opening but cannot pass through and out of an upper portion of the through opening and the spring is configured to support the upper end plug internal piece within the through opening, the upper end plug internal piece and the through opening forming a substantially gas tight seal at an upper limit of travel of the upper end plug internal piece through the through opening and a gas communication path at a point below the upper limit of travel, the upper end plug internal piece being structured to be permanently sealed to the upper end plug external piece after an interior of the cladding is pressurized.